Super-heterodyning phase measurement for heterodyne interferometry

Min Seok Kim; Jun Young Lee; Seung-Woo Kim

doi:10.1117/12.472241

20 June 2002 Super-heterodyning phase measurement for heterodyne interferometry

Min Seok Kim, Jun Young Lee, Seung-Woo Kim

Proceedings Volume 4777, Interferometry XI: Techniques and Analysis; (2002) https://doi.org/10.1117/12.472241
Event: International Symposium on Optical Science and Technology, 2002, Seattle, WA, United States

Abstract

One of the ever-increasing demands on the performances of heterodyne interferometers is to improve the measurements resolution, of which current state-of-the-art reaches the region of sub-nanometers. So far, the demand has been met by increasing the clock speed that drives the electronics involved for the phase measurement of the Doppler shift, but its further advance is being hampered by the technological limit of modern electronics. To cope with the problem, in this investigation, we propose a new scheme of phase- measuring electronics that reduces the measurement resolution without further increase in clock speed. Our scheme adopts a super-heterodyne technique that lowers the original beat frequency to a level of 1 MHz by mixing it with a stable reference signal generated from a special phase-locked-loop. The technique enables us to measure the phase of Doppler shift with a resolution of 1.25 nanometer at a sampling rate of 1 MHz. To avoid the undesirable decrease in the maximum measurable speed caused by the lowered beat frequency, a special technique of frequency up/down counting is combined to perform required phase- unwrapping simply by using programmable digital gates without 2π ambiguities up to the maximum velocity guaranteed by the original beat frequency.

Citation Download Citation

Min Seok Kim, Jun Young Lee, and Seung-Woo Kim "Super-heterodyning phase measurement for heterodyne interferometry", Proc. SPIE 4777, Interferometry XI: Techniques and Analysis, (20 June 2002); https://doi.org/10.1117/12.472241

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